The present invention relates to a pin for connecting gears to a supporting member.
More specifically, the present invention relates to a supporting pin which may be used to advantage, though not exclusively, in epicyclic gear trains for transmitting severe loads in general, and in epicyclic gear trains of aircraft transmissions in particular, to which the following description refers purely by way of example.
Aircraft transmissions normally comprise an epicyclic gear train in turn comprising a sun gear, a ring gear, and a number of planet wheels interposed between the sun and ring gears and supported on a planet carrier.
In most applications, the planet carrier comprises two substantially platelike elements positioned facing each other on opposite axial sides of the planet wheels, and connected integrally to each other by a number of the gear train in relative motion.
To eliminate the above drawbacks, dedicated supporting pins are used, which have opposite elastic end portions of the same size, which deform elastically alongside deformation of the platelike elements and respective tenons to ensure the gears mesh correctly at all times. Also, between the carrier and the supporting body, provision is and must be made for a load balancing assembly, which comprises a number of axial arms connected integrally to the supporting body; and, for each arm, a respective connecting member lying in a plane perpendicular to the sun and ring gear axes and through the center lines of the planet wheels.
Known balancing assemblies of the above type are particularly complex, are extremely expensive to both produce and maintain, and, being highly stressed, are subject to frequent breakdowns and malfunctioning.
It is an object of the present invention to provide a supporting pin designed to solve the aforementioned problems in a straightforward, low-cost manner.
According to the present invention, there is provided a pin for connecting a gear to a supporting member; the pin having a respective axis, and comprising a first and a second longitudinal end portion connectable to said supporting member; a first intermediate portion extending from said first end portion; and a second intermediate portion extending from said second end angularly equally spaced cross members or tenons normally integral with both the platelike elements. Each of the planet wheels is connected to the carrier by a respective supporting pin, the opposite ends of which are each connected to a respective platelike element, and to which the respective planet wheel is in turn normally connected via the interposition of a bearing, normally a friction bearing.
During operation of the gear train, the carrier is stressed by forces which, in some cases, result in deformation of the carrier and, in particular, in displacement of the two platelike elements with respect to each other.
Displacement of the platelike elements in turn results in deformation of both the tenons and the supporting pins, the axes of which pass from an ideal work or rest condition parallel to the axes of the sun and ring gears, to a real or critical work condition in which they form, with the sun and ring gear axes, an angle of other than zero and which varies according to the intensity of the forces transmitted.
Deflection of the pin axes and, hence, of the respective planet wheel axes with respect to the ring and sun gear axes results in uneven distribution of the contact pressures between the planet wheel teeth and those of both the sun and ring gear, which in turn results, not only in general malfunctioning of the gear train, but also in rapid wear of the contacting parts of portion; characterized in that said first and said second intermediate portion differ from each other in size and in flexural strength.